A converted form of the normal cellular
prion protein (PrP) accumulates in the brains of sheep with
scrapie. We describe an immunohistochemical method for identifying
scrapie-associated PrP (PrPSc) in
periodate-lysine-paraformaldehyde-fixed brain tissue, which provides adequate preservation of tissue morphology. After pretreatment of tissue sections with
formic acid and hydrated autoclaving, we located PrPSc in the brains of 50 sheep with natural
scrapie by use of antipeptide
antisera raised against ovine PrP. No PrP was seen in 20 sheep without histopathologic signs of
scrapie. PrPSc that did not
stain for
amyloid was present in the cytoplasm and at the cell membrane of both neurons and astrocytes. Large amounts of PrPSc were seen at the cell membrane of neurons in the medulla oblongata and pons, whereas PrPSc accumulated at the cell membrane of astrocytes of the glial limitans in all brain regions. PrPSc that stained for
amyloid was located in the walls of blood vessels and perivascularly in the brains of 32 (64%) of 50 sheep, mainly in the thalamus and never in the pons or medulla oblongata. No apparent topographic relationship existed between PrPSc that stained for
amyloid and PrPSc accumulation associated with neurons or astrocytes. In all
scrapie-affected sheep, PrPSc was present in brain regions with vacuolation, but it could also be detected in regions with minimal or no vacuolation. We conclude that the immunohistochemical detection of PrP can be an important confirmative test in
scrapie diagnosis.